Voltmeter for vacuum tubes



Sgpt. 10, 1935. A. B. DU MONT VOLTMETER FOR VACUUM TUBES Filed Sept. 19, 1932 NVENTOR 4% fildbw' A TTOR/VE y Patented Sept. 10, 1935 UNITED STATES PATENT OFFICE 2,014,106 I 1 VOLTMETER FOR VACUUM TUBES Allen B. Du Mont, Upper Montclair, N. J.

Application September 19, 1932, Serial No. 633,748

4 Claims. (01. 250-275) the electrodes of a vacuum tube although it may have other applications.

In certain applications of vacuum tubes it is desirable to note the voltage between the electrodes. This is particularly true in connection with the uses of such tubes in radio transmitting stations. It is inconvenient and costly to provide a voltmeter separate from the tube for ascertaining the desired voltage.

It is therefore an object of the present inven tion to provide a means for indicating the desired voltages which shall depend for its operation upon the electronic stream produced in the tube and which may be incorporated in the tube itself although it may be found convenient to mount one or more parts of the device independently of the tube.

A further object of the invention is to utilize electronic streams produced in tubes of the audion type for indicating the voltage whereby the tube not only functions in the usual manner of an audion tube but also provides a means of indicating voltage, current, etc.

A further object of the invention is to make use of an electronic stream produced in vacuum tubes of the audion type whereby the tube not only functions for the usual purposes of tubes of that type but also provides the cathode rays for operating upon fluorescent material for various purposes.

A further object of the invention is to utilize an electronic stream produced in a tube of the audion type to act upon fluorescent material whereby the tube functions for the purposes of the tube of the audion type and also furnishes the electronic stream for acting upon the fluorescent material, and further providing means responsive to any conditions desired for deflecting the electronic stream. acting upon the fluorescent material whereby the luminosity created in the fluorescent material by the electronic stream may be shifted as desired.

Other and ancillary objects of the invention will appear hereinafter.

In the accompanying drawing which illustrates the invention:--

Fig. 1 is a vertical section on the line l-l of Fig. 3 through a vacuum tube equipped with the invention;

Fig. 2 is a side elevation of the apparatus of Fig. 1 viewed from the left of Fig. 3;

Fig. 3 is a section on the line 3-3 of Fig. 1;

Fig. 4 is a vertical axial section, similar to Fig.

- between which it is desired to note the poten- 1, of a modified form of tube adapted to indicate a plurality of voltages between electrodes of the tube, the plurality of voltages being indicated by a single cathode beam, such view being on a smaller scale than Figs. 1, 2 and 3 and partly 5 broken away;

Fig. 5 is a section on the line 55 of Fig. 4;

Fig. 6 is a side elevation of the tube shown in Fig. 4, viewed from the right hand of that figure;

Fig. 7 is an axial sectional view, partly broken 10 away, similar to Fig. 4, of a modified form of tube adapted to indicate a plurality of voltages between electrodes of the tube by means of a plurality of cathode beams corresponding respectively to the voltages to be indicated; and

Fig. 8 is a side elevation, partly broken away, of the tube as shown in Fig. 7 viewed from the right hand.

Referring to the drawing, and first to Figs. 1,

2 and 3, the apparatus comprises a vacuum tube 20 of the audion type having-an envelope I of glass .evacuated to the order of 1 millionth of an atmosphere. Contained within the envelope, and mounte'd upon a suitable stem, is the electron emitting, such as a suitable thorium coated, filament 2, which is enclosed by a, helical coil 3 of wire constituting the grid andsurrounding the filament and grid, is a metal tube 4 constituting the plate.

As is well known in the operation of audion tubes for the various purposes to which they are adapted, a source of direct current. voltage is connected with its plus terminal to the plate 4 and its minus terminal connected with the filament 2. The filament being heated by passing a suitable current through it as is well understood, a stream of electrons will flow from the filament to the plate, the grid exercising a modifying influence upon this stream according to the results desired to be produced as is well understood in connection with the use of tubes of the audion type.

In the plate 4 is formed a small hole 5 which communicates with a tubular member 6 mounted upon the plate. A stream of electrons being a 45 portion of the electrons moving from the filament to the plate, will be projected through the hole 5 and tube 6 in a beam or pencil which impinges against the fluorescent strip 1 of material adapted to fluoresce under the action of the electronic or cathode ray or beam. Upon opposite sides of the cathode ray are deflection plates 8 and 3 respectively connected to the electrodes tial, in this case the deflection plate 8 being connectedtothetubelandthedeflectlonplate Obeingconnectedwiththefllament.

with no voltage ontheplates [and I the luminousspot createdintheflnorucent material bythecathodebeamwillbedirectlyoppositethe tubelandthedeflectionottheray,andconsequently oitheluminous spot. will, at other times, beinaccordancewiththepotentialdiflerenceor voltagebetweentheplateslandl. Thedeflection of the cathode ray and therefore the positionoi theluminous spotonthe fluorescent materialwillbemeasureoithevoltagebetwemthe platelandthefllamentl.

The fluorescent material, it will be observed, ismounted upon theinsidecithe envelope I and adjacent tothepath oithespohandrupon the outside of the envelope, may be etcheda scale ll calibratedinvcltssothatthe voltage between theelectrodesi'andlmaybereaddirectlyin volts from the positional theiuminous spot. Insteadoietchingthescaleupontheenvelopeit maybemadeuponapieceoitransparentor translucentpaperwhichisthensecuredinposition on the bulb or envelope.

A suitable fluorescent material for use as describediszincsilicatewhichgivesagreenlight under the action 0! the electronic stream.

Itmaybethatitwouldbedesirabletocall special attention to a maximum permissible voltage or to other critical values. To this end fluorescent material giving a diflerent colored light under the cathode rays from that ordinarily appearing,maybe insertedatthe desiredpoints. Thus, at the upper end of the strip I of zinc silicate is placed some calcium tlmgstate I l which receives the impact of the cathode ray when the voltage has exceeded the maximum allowable. The luminous color of the calcium tungstate will beblueso thattheexistenceoithebluelight will indicate that the maximum permissive volt age has been reached or passed.

It will be observed that the cathode beam and consequently the spot on the fluorescent screen will faithfully follow variations. in the voltage,

the shitting of the spot being instantaneous with any change in voltage. In other words thereis no time lag between the change in voltage and the movement or the indicating spot so that all changes in voltage, including peak voltages that occur during modulation, are indicated. This could not occur with voltmeters having moving partsowingto themechanicalinertiaotthose parts.

The intensity of luminosity of the spot also aflords an indication of the merit flowing from the filament to the plate.

Referring now to Figs. 4, 5 and 6, the tube therein shown is of the audion type comprising a glass envelope I, a heated filament I, the grid 8' and the plate 4' and in this plate is a hole 5' communicating with'a tubular member t secured to the plate. The beam of electrons pro jected through this hole and tube against the fluorescent screen or strip 1' has the pair oi! plates and II respectively above and below it. 90 removed from the pair of plates II and II are the plates l3 and II on opposite sides of thepathoi' the beam. Thedeflectionplate II is connected by a conductor [5 with the plate 4', the deflection plate I4 is connected with the grid 3' by a conductor It and the two deflection plates l2 and I! are connected together and to the fllament 2' by the conductor ll. Any voltage between the filament andthe plate I is impressed upontheplates II and llandthecatbodebeam is deflected vertically in accordance with such volhm-whileanyvoltagebetweenthefllammt and the grid is impressed upon the deflecting plates "and llandthecathodebeamiahorizontaily deflected accordingly- The horizontal deflectionot thebeamistherei'oreameasm'ed' the voltage between the grid and the fllament, andtheverticaldeflectionoithebeamisa measure of the voltage between the fllament andtho plate. Inanypoaitionoithelightspotocca-m sionedby theimpingement oi'the cathodebeam upon the screen 1' its horizontal deflection (the voltage between the grid and filament) can be read upon the voltage calibrated scale I! etched Imontheoutersuri'ace oi'theglaasenvelope,and l the vertical deflection of the beam (the voltage betweentheplatel' andthefllament) maybe read ulizon thesimiiarly etched voltage calibrated Refen-ingtoI'lgs.'7and8the audiontypetubc U comprising the glass envelope I", the heated filament the and s" and the plate 4" has a pluralityofseparated holes Zlandll connected respectively with tubes 22 and 23 mounted in the plate. There will be projected through each of thesetubesastreamoi'electronsconstitutinga cathodebeam, each oithesebeamsbeingadapted t0 im upon the fluorescent screen 'I" at 6111818111; P ints and produce a light spot for each beam. Arranged respectively above and below 3 the beam through the tube flare the deflection plates 24 and 25, the deflection plate 2| being connected through the conductor 28 with the fllamentandthedeflectionplate "being connected by the conductor 21 with the plate I". 35 Any voltage between the fllament and the plate 4" therefore will be impressed upon the deflection plates II and 25 which will deflect the cathode beam in proportion, thereby deflecting thelightspotproduoeduponthescreen'Winm proportion to the voltage, the deflection of this lightspotbeingreaduponascale 28 calibrated involts,suchscalebeingetchedupontheexterior of the glass envelope or applied in other suitable ways. 45

Upon opposite sides of the cathode beam through the tube 23 are the deflection plates 2! and 3|, the plate 2! being connected through the conductor 2 with the filament and the plate 3| being connected by the conductor it with the 5 grid. Any voltage between the fllament and grid will therefore be impressed upon the plates 29 and3l,thebeam anditslightspotonthe screen 1"deflected accordingly and the voltage between thefllamentandgridtathedeflecflonoithex light spot, maybe read upon thevoltage calibrated scale 32.

While the invention has been illustrated in what are considered its best applications it may have other embodiments without departing from 30 its spirit and is not therefore limited to the structures shown in the drawing.

What I claim is:

1. The combination with a vacuous envelope of electrodes therein, certain of said electrodes be- 5 ing adapted to produce a stream of electrons, and deflecting plates for said stream respectively connected to the electrodes within said envelope betweenwhich the voltage istobeobserved.

2. The combination with a vacuous envelope, 70 of electrodes therein, certain oi. said electrodes being adapted to produce a stream 01 electrons, deflecting plates for said stream, said plates being respectively connected with the electrodes within said envelope between which the voltage is to be observed, a fluorescent substance adapted to be acted upon by said stream to produce luminosity and a scale for noting the position of the luminous spot produced in said substance by said stream.

3. A vacuum tube of the audion type compris ing a vacuous envelope containing electrodes comprising an electron emitting filament, a grid and a plate, said plate having an opening through which a stream of electrons may pass, fluorescent material mounted upon the inside of said envelope against which said stream is adapted to impinge to produce a. luminous spot and deflecting plates for said stream, said plates being respectively envelope adapted to be acted upon by said stream 10 to produce a luminous spot and plates for defleeting said stream respectively connected with said plate and said filament.

ALLEN B. DU MONT. 

